[GSBN] Cordwood Walls

[Chris Magwood]

Hi Tom,

Although it's something that cordwood enthusiasts don't like to hear, 
the best thing for cordwood walls is to plaster them on both sides. This 
prevents the otherwise huge amount of air leakage that has been evident 
on every cordwood structure I've seen. If not plastered, there is no way 
to prevent the cracks that open up as wood and mortar expand/contract at 
different rates. Surprisingly, the plaster coating seems to hold up very 
well.

Separating the mortar as per John's note is one way to help with the 
thermal performance. We've also done some small scale cordwood buildings 
with hempcrete as the mortar, in which case we use a full mortar bed 
over the width of the wall. This gives the mortar a better thermal 
resistance than the wood in most cases.

In general, hardwoods are avoided in cordwood buildings, as they shrink 
and swell more than lighter softwoods. Cedar is the cordwood of choice 
in our part of the world.

Cordwood is not my first choice, but it can make use of abundant (and 
usually free) wood resources that aren't otherwise considered "useful" 
for building, and can be very low impact and owner-builder friendly.

Chris

On 15-01-07 12:47 PM, John Straube wrote:
> My two cents, I dont have a lot of first hand experience.
> I have heard too many rotten cordwood buildings to be cavalier and am a lot more careful based on those anecdotes.  That said, like straw bale, I would say the approach is to keep the wood dry and allow it to dry.  Big overhangs, capillary break at foundation, stay 8” above grade.
> The r-value of different wood species is pretty well documented.  Expect an imperial R-value of around R-1/inch or a conductivity of 0.1 W/mK.  That said, using mortar around all the wood will trash the R-value by allowing the mortar to conduct heat.  It is not that uncommon in cold climates like the Canadian west for builders to limit the mortar to 2-3” on the inside and the outside and fill the gap in between with sawdust, perhaps lighty lime washed sawdust.  I would expect you would want walls that are at least 16” thick, and perhaps 24” (60 cm) to get good thermal performance. Upgrading windows, ceiling, and foundation should allow you to meet most stringent but sensible energy targets.
>
> Is the cordwood chosen for aesthetics? If not then, add insulation and ventilated and drained cladding on the exterior.  Still looks and works great on the inside.  Or vice versa, add insulation to the inside, but then be more careful about preventing rain wetting on the exterior.
>
> John
> On Jan 7, 2015, at 11:54 AM, Tom Woolley<tom.woolley at btconnect.com>  wrote:
>
>> We have  been asked to advise on building a cordwood building in Northern Ireland
>>
>> The site is in the Sperrin Mountains which has nearly 100% RH all year round
>> average rainfall is well over 1000mm per annum though I am surprised it is not higher
>>
>> There are two issues
>> The building will need to meet reasonably high insulation standards under the building regulations
>> I have found articles claiming that cordwood gives good insulation but I find this hard to accept
>>
>> Log cabins on the west side of Ireland rot in a few years where the end grain is exposed but maybe cordwood would do better?
>>
>> What is the best timber to use ?  Oak is indigenous here but not available commercially
>>
>> Any help much appreciated
>>
>> thanks and Happy New Year
>>
>> Tom
>>
>>
>>
>> Tom Woolley
>> tom.woolley at btconnect.com
>> 80 Church Road
>> Crossgar
>> Downpatrick
>> UK
>> BT 30 9HR
>> 00(44) 28 44 831164
>>
>>
>>
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> John F Straube
> jfstraube at uwaterloo.ca
> www.JohnStraube.com
>
>
>
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-- 
Chris Magwood
Director, Endeavour Centre
www.endeavourcentre.org